Content such as movies and music is provided to users via various media such as a DVD (Digital Versatile Disc), a Blu-ray Disc (a registered trade name), and a flash memory, a network such as the Internet, or broadcast waves. A user can reproduce content by using a recording/reproducing apparatus such as a PC, a portable terminal, or a BD player, or an information processing apparatus such as a television set.
However, the copyrights, distribution rights, and the like of most pieces of content such as music data and image data to be provided to users are held by the creators of the content or distributors. Therefore, when providing content to users, a content provider puts a predetermined usage restriction on the content in many cases.
There have been problems that recording and reproduction can be repeated with some digital recording apparatuses and recording media without degrading images and sound, and the use of unauthorized copies of content such as distributions of unauthorized copies of content over the Internet and distributions of so-called pirated disks is widely spread.
As a specific measure to prevent such unauthorized use of content, there is a content encryption process. This is a process to encrypt content to be provided to users, and allow only authorized users to acquire the encryption key to the content. Such a process is disclosed in Patent Document 1 (JP 2008-98765 A), for example.
The key to be used in decrypting encrypted data is given only to the reproducing apparatuses granted the license to use the content. The license is granted to reproducing apparatuses that are designed to comply with predetermined operation rules such as not to make unauthorized copies. Meanwhile, reproducing apparatuses not granted the license are unable to decrypt encrypted data, not having the key for decrypting encrypted data.
However, even after the above process is performed, it is difficult to prevent users who have made authorized purchases of content from providing others with the key for content decryption acquired from a server. Specifically, there might be a case where the key acquired from the server is put up on the Internet so that the general public can use the key. Where such an action is taken, anyone is allowed to decrypt, reproduce, and use encrypted content by using the leaked key, and unauthorized use of the content becomes rampant.